1. Field of the Invention
The field of the present invention is parallel electrodes, such as capacitors, which are operable in high frequency and/or microwave circuit applications.
2. Background
Radio communication services are becoming so numerous they are reaching the 50 GHz millimeter wave spectrum. As the demand for more telecommunications services increases, and the spectrum becomes increasingly crowded, it is foreseeable that applications in the 50-300 GHz millimeter wave spectrums will be utilized for various telecommunications applications.
Circuits for generating and processing signals in the millimeter wave spectrum present significant challenges to component designers. As the frequencies increase, the quality of the components becomes increasingly difficult to maintain. Specifically, for a basic capacitor utilized in circuits operating at these frequencies, the internal equivalent series resistance (ESR) increases significantly using known dielectrics and construction techniques for microwave capacitors. Upper frequency spectrum applications in the UHF (300 MHz to 3.0 GHz) to SHF (3 GHz to 300 GHz) ranges are limited because dielectric materials used in the capacitors exhibit a significant change in ESR with frequency. As the frequency increases for a typical high frequency capacitor, the ESR can increase from 0.05 ohm at 200 MHz to significantly higher ESR and higher losses can be expected. Additionally, the dielectric constant (∈) also changes as frequencies increase. Thus, capacitors in particular have a practical upper limit in the UHF to SHF frequency spectra when they are constructed with conventional dielectric materials.
One of the more advantageous dielectrics is air. U.S. Pat. No. 6,775,124 and U.S. Pat. No. 7,387,928, the disclosures of which are incorporated herein by reference in their entirety, each disclose capacitors, and methods for making such capacitors, which may be formed with air as the dielectric between the electrode plates of the capacitor. As is seen in U.S. patent publication No. 2008/0130197, the disclosure of which is incorporated herein by reference in its entirety, such capacitors may be stacked in series or parallel to form high capacitance and high voltage capacitors which are capable of operating at high frequencies.
While these types of capacitors can function well for their intended purpose, one drawback from which they may suffer is a hybrid capacitance resulting from a combination of the capacitance from the intended dielectric (i.e., vacuum, air, gas, etc.) with the capacitance from the spacer(s) separating the electrode plates. Such a hybrid capacitor, while useful in many applications, may suffer from unwanted intrinsic limitations, degradations, performance losses, and/or RF losses, among other things, when used in circuits operating in the upper GHz range.